Lapping fixture reference plate assembly

ABSTRACT

The reference plate assembly includes a horizontal reference plate having three circumferentially spaced apart vertical apertures. Insert units are vertically adjustably mounted in the apertures with the plane of the upper ends of the insert units lying below the plane of the upper surface of the plate and parallel to the plane of the lower surface of the plate. One reference plate assembly may be used interchangeably with any number of cooperating fixtures; any number of reference plate assemblies may be used interchangeably with one cooperating fixture.

United States Patent 11 1 1111 3,898,770

Benz et al. Aug. 12, 1975 [5 LAPPING FIXTURE REFERENCE PLATE 726,851 3/1955 United Kingdom 51/131 ASSEMBLY [75] Inventors: Ernest A. Benz; James V. Keefe, Prim y ner-Owe" M. Simpson both of Park Ridge, Ill, Attorney, Agent, or Firm.lohnson, Dienner, Emrich W [73] Assignee: Speedfam Corporation, Des Plaines, & agner Ill.

[22] Filed: Nov. 25, 1974 ABSTRACT [21] Appl. No.: 526,612 The reference plate assembly includes a horizontal reference plate having three circumferentially spaced apart vertical apertures. insert units are vertically adjustably mounted in the apertures with the plane of the upper ends of the insert units lying below the [58] Field of Search 51/125, 129, 131 plane of the pp Surface of the plate and parallel to 56] References Cited the plane of the lower surface of the plate. One reference plate assembly may be used interchangeably with UNITED STATES PATENTS any number of cooperating fixtures; any number of 0 ,16 5/1963 Boettchef 51/131 reference plate assemblies may be used interchange- 3,388,506 6/1968 Boettcher 51/129 ably with one Cooperating fixture.

FOREIGN PATENTS OR APPLICATIONS 359,372 2/1962 Switzerland 51/129 4 Claims, 6 Drawing Figures LAPPING FIXTURE REFERENCE PLATE ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to lap limiting fixture means for predeterrnining the extent of lapping of workpieces positioned on a rotating lapping disc of a lapping machine.

2. Description of the Prior Art Lap limiting fixture means, of the general type to which the present invention pertains, is disclosed in US. Pat. No. 3,090,169. This type of fixture means comprises a reference plate which is engageable with workpieces, and a surrounding fixture which is urged downwardly by a pressure plate and which is engageable with the lapping disc to arrest downward movement of the fixture means. Three adjustable screws carried by the fixture bear against the upper surface of the reference plate whereby the plate is adjustably positioned within the fixture. The reference plate is retained in place by a separate screw.

The foregoing prior art reference plate is not adapted for repeated mounting and demounting relative to a given fixture, nor for interchangeable use with different fixtures. To accommodate such usage, the upper surface of the reference plate would have to be machined absolutely parallel to the lower surface thereof. Further, the reference plate would have to be protected against damage whereby to maintain absolute parallelism. Alternately, the reference plate would have to be readjusted within the fixture on each occasion of reassociation. However, these operations are expensive,

'- time-consuming and impractical. Hence, the reference plate is substantially confined to continuous use with a single fixture to which it has once been adjusted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reference plate assembly which is especially adapted for repeated mounting and demounting relative to a given fixture, and for interchangeable use with different fixtures.

The reference plate assembly of the present invention includes a horizontal reference plate having an upper surface, a lower workpiece engaging surface, and three circumferentially spaced apart vertical apertures open at their upper ends. Insert units are vertically adjustably mounted in the apertures with the plane of the upper ends of the insert units lying below the plane of the upper surface and parallel to the plane of the lower workpiece engaging surface.

With this arrangement, the upper surface of the reference plate need not be machined or maintained absolutely parallel to the lower surface. Once'the insert units have been properly adjusted, the reference plate assembly may be intermittently used with any one of a number of fixtures in which the adjustable screws for engagement with the insert units have been adjusted with the plane of the lower ends of the screws parallel to the plane of the lower surface of the fixture engageable with the lapping disc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial elevational view, with portions being broken away and shown in section, of a typical lapping machine and lap limiting fixture means embodying the principles of the present invention;

FIG. 2 is a plan view of one of the lap limiting fixture means shown in FIG. 1;

FIG. 3 is a plan view of the reference plate assembly of the lap limiting fixture means of FIG. 2;

FIG. 4 is a sectional view taken substantially along the line 4-4 in FIG. 2 looking in the direction indicated by the arrows;

FIG. 5 is a sectional view taken substantially along the line 5-5 in FIG. 2 looking in the direction indicated by the arrows; and

FIG. 6 is a sectional view taken substantially along the line 66 in FIG. 2 looking in the direction indicated by the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is indicated generally by the reference numeral 10 a typical lapping machine with which lap limiting fixture means embodying the principles of the present invention may be associated. The lapping machine 10 includes framework with a tubular base or housing 12 which provides support for a horizontal lapping disc 14. Surrounding the lapping disc 14 is a staging table 16 from which workpieces can be moved onto the lapping surface of the lapping disc 14 and to which they can be returned when the lapping operation is completed. Selective rotation of the lapping disc 14 about a vertical axis is effected by drive means (not shown) mounted within the housing 12 and having an output shaft 18 connected to the underside of the lapping disc 14 by means of a hub member 20.

Suitably secured to the opposite sides of the housing 12 are the lower ends of vertical columns 22. Extending between the upper ends of the columns 22, above the lapping disc 14, is a horizontal bridge member 24 provided with four lateral arms 26, only two of which are shown. Each of the arms 26 has a vertical bore for receiving the spindle or piston rod 28 of a pneumatic assembly 30 operated by variable pressure. The lower end of each spindle 28 is joumaled in the center of a circular weight or pressure plate 32. The pressure plates 32 fit, with slight clearance, within truing and retaining rings 34 resting on the lapping disc 14.

Arranged within each of the truing and retaining rings 34 beneath the associated pressure plate 32 is lap limiting fixture means 36 embodying the principles of the present invention. As shown in FIGS. 2, 4, 5 and 6, the fixture means 36 includes a reference plate assembly 38 surrounded by a fixture assembly 40.

The reference plate assembly 38 comprises a horizontal circular reference plate 42 having an upper surface 44 and a lower workpiece engaging surface 46. The reference plate 42 is formed with three circumferentially spaced apart vertical internally threaded apertures 48 surrounded by recessed annular shoulders 50 (FIG. 4), three circumferentially spaced apart vertical openings 52 surrounded by recessed annular shoulders 54 (FIG. 5), and a pair of diametrically opposed bores 56 (FIG. 6). Vertically adjustable insert units 58, as shown in FIGS. 3 and 4, are mounted in the apertures 48. Each insert unit 58 comprises an externally threaded main body 60 threadingly engaged in the associated aperture 48, and a hardened metal insert 62 secured in the upper end of the main body 60. Lock nuts 64 are threaded on the main bodies 60 below the plane of the upper plate surface 44, and are engaged with the recessed annular shoulders 50 for retaining the insert units 58 in any preset position. As shown in FIGS. 3 and 5, latch washers 66, having oval slots 68, are secured below the plane of the upper plate surface 44 against the recessed annular shoulders 54.

The fixture assembly 40 comprises a horizontal annular ring-like fixture 70 having an upper surface 72 and a depending annular rim portion 74. As shown in FIGS. 2 and 4, the fixture 70 is formed with three circumferentially spaced apart vertical threaded openings 76 which receive threaded adjustment screws 78, and three radial threaded openings 80 which are aligned with the openings 76 and which receive threaded set screws 82. As shown in FIGS. 2 and 5, the fixture 70 is also formed with three circumferentially spaced apart cut-outs 84 in which are mounted latch units 86 each comprising a latch stem 88 provided at its upper end with a latch handle 90 and provided at its lower end with a cam lobe 92. The latch units 86 are urged upwardly by springs 93. As shown in FIGS. 2 and 6, the fixture 70 is further formed with a pair of diametrically opposed bores 94 in which are secured locating pins 96. As shown in FIGS. 2, 4 and 6, the fixture rim 74 is formed with a plurality of circumferentially spaced apart arcuate pockets 98 in which are secured, as by an epoxy cement 100, arcuate pad members 102 of wear resistant material such as boron carbide. The pad members 102 are mounted with their lower surfaces in a common plane. Extending across the fixture 70, as shown in FIGS. 2 and 5, is a recessed handle 104.

Prior to mounting of the reference plate assembly 38 within the fixture assembly 40, the insert units 58 are adjusted so that the plane of the upper ends of the inserts 62 lies below the plane of the upper plate surface 44 and parallel to the plane of the lower workpiece engaging surface 46, and the adjustment screws 78 are adjusted so that the plane of the lower ends of the screws 78 lies parallel to the plane of the lower surfaces of the pad members 102. During mounting, the fixture assembly 40 is placed over the reference plate assembly 38, the latch units 86 are pivoted from the positions shown in FIG. 2 to align the cam lobes 92 lengthwise of the oval slots 68, the locating pins 96 are aligned with and inserted in the plate bores 56 while the latch units 86 are depressed for moving the cam lobes 92 through the oval slots 68, the latch units 86 are pivoted back to the positions shown in FIG. 2 for disposing the cam lobes 92 below the latch washers 66, and then the latch units 86 are released. In this condition, the spring biased latch units 86 serve to maintain the inserts 62 in engagement with the adjustment screws 78 whereby the plane of the lower plate surface 46 is disposed parallel to the plane of the lower surfaces of the pad members 102.

After the reference plate assembly 38 has been mounted within the fixture assembly 40, workpieces 106 and the fixture means 36 are confined within a truing and retaining ring 34 and moved into position beneath a pressure plate 32. With the reference plate 42 bearing against the workpieces 106 under the weight of the fixture means 36 and pressure plate 32 and the pressure exerted by the pneumatic assembly 30, the lower surfaces of the pad members 102 are initially spaced from the upper surface of the lapping disc 14. The amount of material that will be removed from the workpieces 106 is determined by the vertical distance between the plane of the lower surfaces of the pad members 102 and the upper surface of the lapping disc 14, while the ultimate vertical dimension of the Workpieces 106 is determined by the vertical distance between the plane of the lower plate surface 46 and the plane of the lower surfaces of the pad members 102.

To lap the workpieces 106, the lapping disc 14 is rotated, and a freely flowing mixture of abrasive particles and an oil carrier is fed to the lapping disc 14. As lapping of the work pieces 106 proceeds, the lower surface of the pad members 102 move closer to the lapping disc 14. When the lower surfaces of the pad members 102 engage the lapping disc 14, downward movement of the fixture means 36 is arrested and lapping of the workpieces 106 ceases automatically even though operation of the lapping machine continues. As will be appreciated, a lap limiting fixture means 36 may be arranged within each of the truing and retaining rings 34 on the lapping disc 14.

To separate the fixture assembly 40 from the reference plate assembly 38, the latch units 86 are pivoted from the positions shown in FIG. 2 to align the cam lobes 92 lengthwise of the oval slots 68, and the fixture assembly 40 is then simply raised thereby withdrawing the cam lobes 92 through the oval slots 68.

By reason of the described construction of the reference plate assembly 38, the plate assembly 38 may be mounted and demounted relative to a given fixture assembly 40 as may be required, and may be transferred from one fixture assembly 40 to another, without readjustment on each occasion. Correspondingly, a series of reference plate assemblies 38 may be used sequentially with a single fixture assembly 40. When a series of reference plate assemblies 38 are used, the insert units 58 of each assembly 38 are adjusted as above described, with the planes of the upper ends of the inserts 62 and the planes of the lower workpiece engaging surfaces 46 being spaced the same distance. When a series of fixture assemblies 40 are used, the adjustment screws 78 of each assembly 40 are adjusted as above described, with the planes of the lower ends of the screws 78 and the planes of the lower surfaces of the pad members 102 being spaced the same distance.

While there has been shown and described a preferred embodiment of the present invention, it will be understood by those skilled in the art that various rearrangements modifications may be made therein without departing from the spirit and scope of the invention.

The invention claimed is:

1. For use in lap limiting fixture means, a reference plate assembly comprising a horizontal reference plate having an upper surface, a lower workpiece engaging surface, and three circumferentially spaced apart vertical apertures open at their upper ends; and insert units vertically adjustably mounted in said apertures with the plane of the upper ends of said insert units lying below the plane of said upper surface and parallel to the plane of said lower workpiece engaging surface.

2. The reference plate assembly of claim 1 wherein said apertures are provided with internal threads, and said insert units are provided with external threads threadingly engaged with said internal threads.

3. The reference plate assembly of claim 2 wherein said insert units each comprise a main body provided with said external threads, and a hardened insert secured in the upper end of said main body.

4. The reference plate assembly of claim 3 wherein said reference plate is formed with recessed annular shoulders about said apertures, and including lock nuts threaded on said main bodies below the plane of said upper surface and engaged with said recessed annular shoulders. 

1. For use in lap limiting fixture means, a reference plate assembly comprising a horizontal reference plate having an upper surface, a lower workpiece engaging surface, and three circumferentially spaced apart vertical apertures open at their upper ends; and insert units vertically adjustably mounted in said apertures with the plane of the upper ends of said insert units lying below the plane of said upper surface and parallel to the plane of said lower workpiece engaging surface.
 2. The reference plate assembly of claim 1 wherein said apertures are provided with internal threads, and said insert units are provided with external threads threadingly engaged with said internal threads.
 3. The reference plate assembly of claim 2 wherein said insert units each comprise a main body provided with said external threads, and a hardened insert secured in the upper end of said main body.
 4. The reference plate assembly of claim 3 wherein said reference plate is formed with recessed annular shoulders about said apertures, and including lock nuts threaded on said main bodies below the plane of said upper surface and engaged with said recessed annular shoulders. 